1. Technical Field
Embodiments disclosed herein relate to the field of touch sensors and, more specifically, to improving the response at the edges of the sensing area.
2. Description of Related Art
Modern electronic devices often have touch sensors to receive input data. There are a variety of types of touch sensor applications, such as touch sensors, digitizers, touch buttons, touch switches, touch scroll bars, and other similar devices.
Conventional touch sensors based on capacitive coupling use conductive plates typically made of Indium Tin Oxide (ITO) or some other transparent material that is electrically conductive. Several conductive elements separated by a dielectric may be placed in the plane of a sensor panel to detect the position of a touch. Typically, capacitive touch sensors require multiple layers of Indium Tin Oxide (ITO) to detect multiple touches. Some conventional touch sensors may use a single ITO layer, but they are not capable of determining the location of multiple simultaneous touches in more than a single direction due to the way the single ITO layer is disposed on the touch sensor. Moreover, touch sensors using a single ITO run into accuracy and precision issues for two-dimensional (2D) positioning. This typically occurs due to the conventional geometries used for the conductive elements in the ITO layer. There are conductive elements that produce more accurate 2D location by using new geometries. Examples of conductive elements using new geometries are shown in U.S. patent application Ser. No. 12/543,277, filed Aug. 18, 2009 and assigned to Integrated Device Technology, Inc., which is incorporated herein by reference in its entirety. These conductive elements using the new geometries result in a linear change of capacitance as a touch moves from one conductive element to an adjacent conductive element. While these conductive elements have been successful, there may be a loss of location accuracy at the edges of the sensor panel where linearity of the capacitance changes may fail. The accuracy is typically less in these areas because the conductive sensing elements are measuring only a half of a touch at edges, and only a quarter of a touch at the corners. However, accuracy at the edges and corners of the sensor panel is important as these areas may be used for common important functions such as scrolling or closing an application or file.
What is needed is a touch sensor that more accurately determines the position of touches on edges and corners of a touch-sensitive panel.